Since medical data security has become a growing public concern, a considerable number of schemes have been published for secure medical data sharing and privacy preservation [1]}, [2]}, [3]}, [4]}, [5]}, [6]}, [7]}, [8]}, [9]}, [10]}, [11]}, [12]}, [13]}. For instance, most research in protecting medical data have emphasised the use of cryptographic methods such as CP-ABE and KP-ABE [6]}, [9]}, [5]}, [10]}, [12]}, [19]}. The system architecture proposed in [2]} is based on a successor of CP-ABE and Role-Based Access Control (RBAC) to protect EHR stored in the hybrid cloud with direct and indirect access. In Li et al.'s KP-ABE based model [8]}, the data owner needs to trust the key issuer because they are only inserting a set of descriptive attributes into the data using KP-ABE, but they do not know who will be accessing their data [22]}. Xu et al. [5]} presented a practical dual-policy ABE scheme for EHR systems that combines the advantages of CP-ABE and KP-ABE with support for user revocation. In addition, Belguith et al. [10]} proposed a multi-authority CP-ABE scheme that delegates expensive computing tasks to cloud servers, and their scheme also prevents collusion between the authorities.
